LeetCode题解之Convert Sorted List to Binary Search Tree

1、题目描述

2、题目描述

使用快慢指针寻找链表中间值。

3、代码

 TreeNode* sortedListToBST(ListNode* head) {
         if (head == NULL)
             return NULL;

         ListNode *mid = findmid(head);

         TreeNode *node = new TreeNode(mid->val);

         if (head == mid)
             return node;

         node->left = sortedListToBST(head);
         node->right = sortedListToBST(mid->next);
         return node;

     }

     ListNode *findmid(ListNode* left)
     {
         ListNode *preptr = NULL;
         ListNode *slow = left;
         ListNode *fast = left;

         while (fast != NULL && fast->next != NULL) {
             preptr = slow;
             slow = slow->next;
             fast = fast->next;
             fast = fast->next;
         }
         if (preptr != NULL)
             preptr->next = NULL;
         return slow;
     }